One of the most important requirements of a next generation wireless communication system is to support a required high data rate. For this, various techniques such as multiple input multiple output (MIMO), cooperative multiple point transmission (CoMP), relay, etc., have been under research, but the most fundamental and reliable solution is to increase a bandwidth.
However, a frequency resource is in a saturation state at present, and various schemes are partially used in a wide frequency band. For this reason, in order to ensure a broadband bandwidth to satisfy a required higher data rate, a system is designed such that a basic requirement which requires separate bands capable of operating respective independent systems is satisfied, and a carrier aggregation (CA) is introduced. In concept, the CA aggregates a plurality of bands into one system. In this case, a band that can be independently managed is defined as a component carrier (CC).
To support growing transmission capacity, the 3GPP LTE-A or the 802.16m has recently expanded its bandwidth to 20 MHz or higher. In this case, a wideband is supported by aggregating one or more CCs. For example, if one CC corresponds to a bandwidth of 5 MHz, four carriers are aggregated to support a bandwidth of up to 20 MHz. As such, a carrier aggregation system uses a plurality of CCs, and in this sense, can be called a multi-carrier system.
A CC allocated to the terminal in the multi-carrier system can be changed for various reasons such as a channel environment, a transmission data amount, etc. For example, three CCs can be allocated in such a manner that one CC is added to the terminal while communication is performed by allocating two CCs to the terminal. Alternatively, two CCs can be allocated in such a manner that one CC is removed while communication is performed by allocating three CCs.
As such, when there is a change in the CCs allocated to the terminal, downlink control information transmitted by a base station can be reconfigured from a configuration not including a carrier indication field to a configuration including the carrier indication field. In this case, a message for indicating a reconfiguration in the carrier indication field and a message for reporting the completion of the reconfiguration in the carrier indication field are signaled between the base station and the terminal. However, if an error occurs in this process, there may be a case where the terminal is not able to correctly decode downlink control information transmitted by the BS.